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c++ctaylor-series

Problems while calculating value of sine with Taylor series

I'm trying to calculate

sin x

Using the following code.

#define PI 3.14
double ans;
double input1;

void toRad() {
    input1 = input1 * PI / 180.0;
}

void sine(void) {
    toRad();
    ans = input1;
    int i = 1;
    for (; i < 15; i++) {
        if (i % 2 == 0)
            ans = ans + (ans * input1 * input1) / 2 * i * (2 * i + 1);
        else
            ans = ans - (ans * input1 * input1) / 2 * i * (2 * i + 1);
    }
    printf("%lf", ans);
}

I used iterative operations instead of pow and factorial functions to get more precise values and more iterations.

But, for some reason, I got different outputs like -4000000E. What can be the problem of this code?

Solution

  • you have made a small mistake in writing the logic.check yourself until i=4.

         if (i % 2 == 0)
        ans = ans + (ans * input1 * input1) / 2 * i * (2 * i + 1);
    else
        ans = ans - (ans * input1 * input1) / 2 * i * (2 * i + 1);

    instead of this you should create a factorial function so that it can be replaced by 

        if (i % 2 == 0)
        ans = ans + (ans * input1 * input1) / factorial(2 * i + 1);
    else
        ans = ans - (ans * input1 * input1) / factorial(2 * i + 1);